1. Field of the Invention
The present invention relates to a cleaning blade, and an electrophotographic image forming apparatus using the same and a process cartridge detachably attached to the image forming apparatus.
2. Description of the Related Art
Conventionally, electrophotographic image forming apparatuses have removed unnecessary transfer residue toner deposited on the surface of an image bearing member such as a photoconductor as a cleaning target member, after having transferred a toner image onto a transfer sheet or an intermediate transfer member, with a cleaning device as a cleaning unit. Well-known as a cleaning member of this cleaning device is one with a reed-shaped cleaning blade, because such a cleaning member can be generally configured into a simple structure and has excellent cleaning performance. This cleaning blade is formed of a reed-shaped elastic blade made of a polyurethane rubber or the like. In the cleaning blade, the base end of the elastic blade is supported on a support member, and the leading end edge portion thereof is thrust against the circumferential surface of the image bearing member, in order to remove any residual toner on the image bearing member by banking it up and scraping it off.
To meet the recent demand for images with higher qualities, there is known an image forming apparatus that uses a toner formed by polymerization or the like to have a small particle diameter and nearly a spherical shape (hereinafter referred to as polymerized toner). This polymerized toner is characterized by a high transfer efficiency compared with conventional pulverized toners, and can meet the above demand. However, it is difficult to remove the polymerized toner sufficiently when trying to remove it from the surface of the image bearing member with a cleaning blade, bringing about a problem that a cleaning failure may occur. This failure is because the polymerized toner, which has a small particle diameter and excellent sphericity, can slip through the slight gap formed between the cleaning blade and the image bearing member.
In order to prevent such slip-through, it is necessary to enhance the abutting force of the image bearing member and the cleaning blade against each other to improve the cleaning performance. However, when the abutting force of the cleaning blade is enhanced, the friction force between the cleaning blade 262, the cleaning blade surface 262b and the image bearing member 23 increases as shown in FIG. 1A, to thereby drag the cleaning blade 262 to the direction to which the image bearing member 23 is moved, to let the leading end edge portion 262c of the cleaning blade ride up. Further, if the cleaning is continued with the leading end edge portion 262c of the cleaning blade 262 ridden up, a local wear will occur at a location that is several μm away from the leading end edge portion 262c of a leading end surface 262a of the cleaning blade 262, as shown in FIG. 1B. If the cleaning is further continued in this state, this local wear will become larger to finally drop off the leading end edge portion 262c, as shown in FIG. 1C. If the leading end edge portion 262c is dropped off, it is no longer possible to clean away the toner properly, leading to a cleaning failure.
Hence, it has been necessary to make the leading end edge portion of the cleaning blade safer from deformation by enhancing the hardness thereof, in order to suppress the riding up of the leading end edge portion. Japanese Patent (JP-B) No. 3,602,898 describes an elastic blade made of polyurethane elastomer, which is provided, on a region thereof including at least the leading end edge portion thereof, with a surface layer made of a resin having a film hardness that is represented by a pencil hardness of from B to 6 H. With the surface layer having a film hardness represented by a pencil hardness of from B to 6 H that is harder than the elastic blade, it is possible to reduce the friction force between the image bearing member and the cleaning blade, which leads to suppression of the riding up of the leading end edge portion of the cleaning blade. Furthermore, because the surface layer with a pencil hardness of from B to 6 H is hard and less likely to deform, it is possible to suppress the riding up of the leading end edge portion of the cleaning blade with a greater effectiveness.
Japanese Patent Application Laid-Open (JP-A) No. 2004-233818 describes a cleaning blade, which is provided on the surface thereof with a cured layer formed by impregnating an elastic blade with a silicone-containing ultraviolet curable material, swelling the ultraviolet curable material, and thereafter subjecting the blade to ultraviolet irradiation. In this way, also by providing a cured layer made of an ultraviolet curable material harder than the elastic blade, it is possible to suppress the riding up of the leading end edge portion of the cleaning blade.
However, even such cleaning blades as described above provided with a surface layer or a cured layer have caused cleaning failures, under strict conditions such as when performing cleaning after continuous formation of solid images that have resulted in a very large amount of powder having been deposited on the image bearing member. This is considered due to the following reasons. That is, because the surface layer or the cured layer is formed all over the longer direction of the elastic blade, the elasticity of the elastic blade may be inhibited by the surface layer or the cured layer. When the elasticity of the elastic blade is inhibited, the abutting pressure of the cleaning blade abutting on the surface of the image bearing member may vary in the longer direction of the cleaning blade, if the image bearing member is decentered or if the surface of the image bearing member has minute undulations, which leads to degradation of followability of the leading end edge portion of the cleaning blade to the image bearing member. When a large amount of toner is banked up by the cleaning blade such as after solid images are formed continuously, a pressing force of the banked-up toner against the cleaning blade is large. Therefore, in the regions where the abutting pressure of the cleaning blade against the image bearing member is low, the abutting state cannot be maintained in these regions when the pressing force of the toner on the image bearing member against the cleaning blade becomes greater than the abutting force of the cleaning blade, to allow the toner to slip through the cleaning blade. A cleaning failure is considered to have occurred as the result of this, under strict conditions such as when performing cleaning after continuous formation of solid images.
In a cleaning blade provided only with a surface layer such as that described in JP-B No. 3,602,898, if the surface layer is thick, the elasticity of the elastic blade is inhibited by the stiffness of the surface layer, and the followability of the leading end edge portion to the surface of the image bearing member is degraded. Therefore, in the configuration that is provided only with a surface layer, it is necessary to make the surface layer having a high hardness thin in order to maintain the followability of the leading end edge portion to the surface of the image bearing member. When the surface layer is thin, the surface layer will be worn in a short time in the elapse of time of use to the extent to expose the elastic blade. When the elastic blade having a lower hardness is exposed to thereby directly contact the surface of the image bearing member, the coefficient of friction between the cleaning blade and the surface of the image bearing member becomes large, to have the leading end edge portion worn largely.
A cleaning blade as described in JP-A No. 2004-233818, on which a cured layer is formed by impregnating an elastic blade with an ultraviolet curable resin and subjecting it to ultraviolet irradiation, has the following problem. That is, when forming a cured layer in a manner to make the hardness of the outermost surface of the leading end edge portion equal to the hardness obtained when providing a surface layer on the surface of the elastic blade, it is necessary to impregnate the blade with so large an amount of an ultraviolet curable material as enough to cover the surface of the elastic blade. When the blade is impregnated with such a large amount of an ultraviolet curable material, the amount of the ultraviolet curable material soaked into the inside of the elastic blade is also large.
When the elastic blade soaked with a large amount of the ultraviolet curable material is irradiated with ultraviolet, the cured layer will be formed to be excessively hard and to an excessive depth, to thereby inhibit the elasticity of the elastic blade and degrade the followability of the leading end edge portion to the surface of the image bearing member. On the other hand, when the amount of the ultraviolet curable material with which to impregnate the elastic blade is reduced in order to maintain the followability of the leading end edge portion to the surface of the image bearing member, it is impossible to cover the surface of the elastic blade completely with the ultraviolet curable material. The outermost surface of the leading end edge portion will be a mixed state of the rubber material of the elastic blade and the ultraviolet curable material, and the hardness of the outermost surface of the leading end edge portion during an initial time after the start of use will be less than when a surface layer is provided. This will increase the friction force between the cleaning blade and the image bearing member, to make it more likely for the leading end edge portion of the cleaning blade to ride up.